Graphene is a two-dimensional layered material structure of carbon. The single-layer graphite has a thickness of about 0.35 nm and has outstanding electrical, optical and mechanical characteristics. Graphite of not more than ten layers is regarded as graphene. Since the successful development of single-layer graphene in 2004, graphene has drawn great attention. Due to its Dirac-Fermi property, linear energy band structure and the highest carrier mobility (200000 cm2 v−1 s-1) among the materials that have been discovered so far, graphene has been widely applied in the field of high-frequency nano-electronic devices. Meanwhile, graphene has remarkable optical characteristics and a flat absorption band from ultraviolet, visible light to infrared bands (from 300 nm to 6 μm); and, its absorption characteristic may be regulated by applying a voltage (Science, Vol. 320, P206), so that graphene may realize wideband high-speed photoelectric conversion. Graphene shows very high interaction with light, so that the absorption of the single-layer graphene (0.34 nm in thickness) in the above wavebands amazingly reaches 2.3% (Physical Review Letters, Vol. 01, P196405; Science, Vol. 320, P1308). However, the effective absorption of single-layer or multi-layer (less than 10 layers) graphene to light is far lower than the efficiency of other bulk materials or quantum well structures.
Recently, more and more researches have focused on the enhancement of the interaction between graphene and light, particularly on light absorption. In 2012, the team of Prof. Mueller in Australia proposed that graphene was placed between two one-dimensional Bragg grating reflectors to enhance the interaction between the graphene and near-infrared light by increasing the photon state density via a microcavity. In comparison to a case without any microcavity, it was found that light absorption was enhanced by 26 times (Nano Letters, Vol. 12, P2773). Meanwhile, in P3808 in the same volume of Nano Letters, another technology for enhancing light absorption by the surface plasmon effect of a metal nanostructure was disclosed, and the experimental results showed that light current in the visible light waveband was increased by 8 times. In 2012, a team of the United States, the United Kingdom and Germany proposed to use a metal microcavity in combination with a transistor structure to improve the sensitivity of a graphene optical detector, and it was found that the light current in the visible light waveband was increased by 20 times (Nature Communications, Vol. 3, P906). In addition, in 2011, using a graphene transistor, scientists in the United States observed the absorption phenomena of THz waves caused by two-dimensional electron gas (Nature Nanotechnology, Vol. 6, P630). As can be seen, detectors based on graphene have shown an ultra-wide working range from visible light to THz waves. Although the above technologies all show a certain degree of enhancement of light absorption of graphene by microcavity, plasmon or other effects, more effective technical solutions need to be further explored in the art due to the complexity of technical processes and the limitations to the performance enhancement.